1. Field of the Invention
The present invention relates to an adjustable surfboard fin fitted into a bottom of a surfboard used in surfing.
2. Description of the Related Art
Surfing is one of marine leisure activities that recently has become a major sport in Japan. Types of surfing include not only ordinary surfing using a surfboard on which a surfer rides, windsurfing using a surfboard with a sail, and bodyboarding using a surfboard called “bodyboard” held in the arms of a bodyboarder. These activities of surfing are similar in that a surfboard is used.
As shown in FIG. 7, a surfboard fin 3 is fitted into a rear-end position on a bottom of a surfboard 1 sunk under water for improving surfboard handling. Although some fixed surfboard fins are known, more surfboard fins are detachably attached to the positions each via a securing member 2 for various reasons such as replacement after damage, wear or the like and change of magnitude according to purposes. The surfboard fin of the latter type will be referred to as “adjustable surfboard fin”, hereinafter.
U.S. Pat. No. 3,564,632, granted in the US that is a leading country in the surfing, relates to a securing structure for securing such an adjustable surfboard fin. It is disclosed in the U.S. Pat. No. 3,564,632 that a groove of a securing member and a bottom of the surfboard fin are both inclined, and that screws are provided in front of and in rear of a bottom member of the surfboard fin and fastened to the securing member, thereby securing the surfboard fin into a suitable position.
Similarly to the invention disclosed in the U.S. Pat. No. 3,564,632, a surfboard fin configured so that only one screw is arranged at one position and a fulcrum pin is arranged at the other position is commercially available. The surfboard fin will be described with reference to FIGS. 8 to 11.
FIG. 8 is a partial longitudinal sectional view of a surfboard showing a fitting portion into which an adjustable surfboard fin is fitted. FIG. 9 is a cross-sectional view of the surfboard in a right-angle direction. FIG. 10 is a perspective view showing principal parts of the adjustable surfboard fin. In FIGS. 8 to 10, reference symbol 1 denotes a surfboard, 2 denotes a securing member into which the surfboard fin is secured, 3 denotes the surfboard fin, 31 denotes a fulcrum pin provided near a rear end of an inserted portion 34 of the surfboard fin 3 inserted into the securing member 2, 32 denotes a fixed screw provided on a front end of the inserted portion 34, and 33 denotes a nut.
FIG. 11 is a partial perspective view of the surfboard 1 showing the securing member 2 and its surroundings. In FIG. 11, reference symbol 21 denotes a longitudinal groove, 22 denotes a transverse groove formed in a sidewall of the longitudinal groove 21, and 23 denotes a notch formed near the center of the longitudinal groove 21.
If the surfboard fin 3 is to be fitted into the surfboard 1, then the fulcrum pin 31 of the surfboard fin 3 is inserted into the securing member 2 from the notch 23, the surfboard fin 3 is moved, and the nut 33 is inserted from the notch 23 similarly to the fulcrum pin 31. Next, the surfboard fin 3 is moved back and forth to be positioned to a desired position, and the fixing screw 32 is fastened to thereby secure the surfboard fin 3 into the desired position. The fulcrum pin 31 and the nut 33 together with the surfboard fin 3 are moved in the transverse groove 22.
As a material of the surfboard 1 and the surfboard fin 3, a light and tough material such as FRP or ABS resin is used in view of portability and a buoyant force when in use, that is, in view of a combination of a weight, a specific gravity, and a strength.
However, as can be understood from FIG. 9, if the surfboard fin 3 is repeatedly attached and detached, then the securing member 2 and/or the inserted portion 34 of the surfboard fin 3 may possibly be worn and deformed, a gap is generated or the surfboard fin 3 becomes unstable. This disadvantageously causes deterioration in steering performance and degradation in safety.